Damping is the absorption of energy, such as vibrational or sound energy, by a material in contact with the source of that energy. Damping vibrational energy from a number of sources such as motors and engines can be desirable.
Viscoelastic materials are often employed for damping applications. Energy is absorbed by the viscoelastic material and converted into heat. Ideally, viscoelastic materials employed for damping are effective over a wide range of temperatures and frequencies.
The viscoelastic nature of materials can be mathematically represented by the formula G*=G′+iG″ where G* is the complex shear modulus, G′ is the elastic or storage modulus, G″ is the viscous or loss modulus, and i=√{square root over (−1)}. The damping effectiveness of viscoelastic materials can be quantified by measuring viscoelastic response to a periodic stress or strain. Results of dynamic mechanical tests are generally given in terms of G′ and G″, where G″ is directly related to the amount of mechanical energy converted to heat, i.e., damping.
The ratio of G″ to G′ is often referred to as tan δ,       tan    ⁢                   ⁢    δ    =                              G          ″                                              G          ′                    which quantifies a material's ability to dissipate mechanical energy versus the purely elastic storage of mechanical motion during one cycle of oscillatory movement. Tan δ can be measured by a dynamic analyzer, which can sweep many frequencies at a fixed temperature, then repeat that sweep at several other temperatures, followed by the development of a master curve of tan δ versus frequency by curve alignment. An alternate method measures tan δ at constant frequency over a temperature range.
In common practice, the tan δ of a material is usually broadened by taking advantage of the glass transition temperature of several materials within a temperature range. Enhancing hysteresis (tan δ) by using superposition of glass transition peaks is not desirable because the modulus of the material drops dramatically at or about the glass transition temperature.
Although numerous compositions are known for damping, there is a need for improved damping compositions that exhibit a high degree of damping over a wide range of temperatures and frequencies without involving glass transition peaks.